1. Field of the Invention
The invention relates to a corrosion inhibited aqueous solution, particularly an antifreeze composition useful as a coolant in a heat-exchange system such as the cooling system of an internal combustion engine.
2. Prior Art
Anitfreeze concentrate compositions adapted to be diluted with water and used as coolants for internal combustion engines generally contain a major amount of a watersoluble alcohol, a buffer capable of maintaining the pH of the diluted concentrate between a pH of about 7.5 to about 11, about 0.5 to 5 percent by weight of additives to inhibit corrosion and foaming during use, and the balance water. The alcohol can be methanol, ethylene glycol, diethylene glycol, glycerol, etc. The additives, besides metal corrosion inhibitors and antifoam agents, can include a water-pump lubricant. As a consequence of the wide variety of metals utilized in contact with the cooling system compositions in an internal combustion engine, a wide variety of inhibitors have been proposed for use in cooling system compositions containing an alcohol. This is because no one inhibitor has yet provided protection for all of the various metals in contact with the cooling system liquid.
Examples of prior art corrosion inhibitors include inorganic compounds such as alkali metal phosphates, borates, molybdates, arsenates, arsenites, nitrates, silicates, nitrites, and chromates, as well as various organic compounds such as mercaptobenzothiazole, tolyltriazole, benzotriazole, piperazine, ethylene diamine tetracetic acid and the reaction product of phosphoric acid or boric acid and an alkanolamine.
Recently, efforts have been made to eliminate the alkali metal nitrates and nitrites from antifreeze compositions as well as amine-corrosion inhibitors such as triethanolamine and diethanolamine. This is because of the possible formation of the carcinogenic nitrosamines which can be formed by the reaction of a second amine and a nitrite. The elimination of nitrates is believed desirable since upon reduction, nitrites are formed which could in turn react with a secondary amine to form the undesirable nitrosamines. The elimination of nitrites and nitrates from antifreeze compositions generally results in greater susceptibility of the metals in contact with such antifreeze compositions to corrode and this is particularly true of iron and steel. Heretofore, antifreeze compositions have been prepared free of alkali metal nitrites and nitrates by incorporating a corrosion inhibitor prepared by the reaction of boric acid, phosphoric acid and a mono-, di- or tri-alkanolamine together with an alkali metal mercaptobenzothiazole. Such compositions, however, have not been entirely satisfactory with respect to the inhibition of corrosion of cast iron and steel in contact with ethylene glycol-based antifreeze compositions as indicated in U.S. Pat. No. 3,350,316. Triethanolamine salts of mono- and dinonylphenol (ethoxylate) phosphate acid esters are also known from U.S. Pat. No. 3,422,166 as corrosion inhibitors for use in metal working operations such as the working of aluminum, iron and steel.
Triethylene diamine, or 1,4-diazaobicyclo-(2.2.2)-octane, is known for use as a catalyst in the preparation of urethanes as disclosed in U.S. Pat. No. 2,939,851. Representative of the prior art use of organic amines as components of corrosion inhibiting compositions for use in protecting metals from corrosion where said metals in contact with aqueous solutions are U.S. Pat. No. 4,130,524 wherein a salt of phosphoric acid and an organic amine, which can be a tertiary monoamine, is disclosed as a corrosion inhibitor useful in the protection of a metallic surface against corrosion. The use of guinuclidine as an inhibitor of iron corrosion under aqueous acid conditions is disclosed by Aramaki in Denki Kagaku 1972, 40(8), pages 556-571. Amine/phosphate compositions useful as corrosion inhibitors are also disclosed in U.S. Pat. No. 3,787,319. These are the reaction products of a phosphate ester and a secondary alkyl alkylene diamine. A three-component corrosion inhibitor system is disclosed in U.S. Pat. No. 3,935,125 which is a mixture of a lower alkyl amine pyrophosphate, an organo phosphonate, and a triazole.